Field of the Invention
The present invention relates to a high frequency discharging method and an apparatus thereof, and a high frequency processing apparatus which are, for example, used for the manufacturing of a thin film element on a semiconductor wafer, or the particle beam source or the plasma source of an analyzer, a heating device, or the like.
An element having a thin film whose components are metal, semimetal, semiconductor, oxide, nitride, arsenic, and the like (hereafter, simply referred to as a thin film element), is applied to main surface portions of various types of products and devices, for example, recording products such as an LSI, a magnetic record, or an optical record, or to communication devices such as a semiconductor laser or a photoelectric transfer element, or to flat-panel displays such as an LCD, or to image pick-up devices such as a CCD, or to energy devices such as a solar battery. This use of thin films is expected to develop even further in the future, as an essential part of miniaturization and enhancement of efficiency of devices.
In a thin film element like this, the miniaturization of the structure thereof and the enhancement of efficiency has been advanced, and the manufacturing process using plasma is important in, for example, etching or CVD processes. Then, the area of a substrate of a object used in the manufacturing process has become larger from the viewpoint of improving productivity.
In order to achieve such a manufacturing process, an inductively coupled type of high frequency plasma apparatus is attracting attention. Usually, this inductively coupled type of high frequency plasma apparatus is arranged such that an antenna shaped like a loop (hereafter, simply referred to as a loop antenna) is arranged outside a vacuum container and an induction field is generated by allowing a high frequency current to flow to the antenna. This induction field is added to the gas in the vacuum container and plasma is created.
The induction field generated by the antenna is added to the gas in the vacuum container through a dielectric window provided in the vacuum container, and high frequency power is coupled with the plasma through the induction field.
There is also an internal antenna type system having a loop antenna arranged inside the interior of the vacuum container and a high frequency current is allowed to flow in the antenna so as to create the plasma. Since the distance between the antenna and the plasma is short, the high frequency power from the antenna to the plasma is efficiently transmitted and plasma with a high density can easily be created.
An example of an internal antenna type plasma processing apparatus used for sputtering is described in Jpn. Pat. Appln. KOKAI Publication No. 7-18433, and an example of this technique used for CVD is described in Jpn. Pat. Appln. KOKAI Publication No. 8-81777.
In this type of inductively coupled type high frequency discharge, an induction field is generated by the high frequency current flowing to the antenna and an electrostatic field is generated between the antenna and the plasma because of the potential of the high frequency voltage on the antenna.
In an external antenna system, a negative direct current self bias voltage arises on the surface of the dielectric window because of the generated electrostatic field. In an internal antenna system, a direct current self bias voltage arises due to the plasma surrounding the antenna itself. This direct current self bias voltage accelerates the ions in the plasma and the dielectric window or the antenna is itself sputtered. The phenomenon of such sputtering appears more noticeably in an internal antenna system since the distance between the antenna and the plasma is short.
The sputtering arises as to the antenna even in the state where the direct current bias voltage is nor applied to the antenna arranged in the interior of the vacuum container. See, for example, the technique described in Jpn. Pat. Appln. KOKAI Publication No. 7-18433.
However, if an internal antenna system is used in a process such as CVD or etching, the sputtered atoms and molecules have an adverse effect on the process as impurities.
That is, as the result of the electrostatic coupling between the antenna and the plasma, a negative direct current self bias voltage arises in the antenna or the dielectric near the antenna, and by the self bias voltage, the ions generated by the discharge are accelerated, and the dielectric or the material of the antenna is sputtered. For example, if the material of the antenna is copper, copper or ionized copper is deposited to adhere to the inner wall of the vacuum container or the object.
Furthermore, in an internal antenna system, the internal antenna is consumed by this sputtering and, therefore, the antenna must be periodically replaced by a new antenna as it is consumed. That is, it is treated as a replacement part.
When creating plasma with a uniform density in a large diameter vacuum container using an external antenna system, a complex and delicate shape of an antenna is often adopted.
On the other hand, in an internal antenna system, an antenna is treated as a replacement part as mentioned above and, therefore, it is required for an antenna to have the simplest possible structure in order to reduce the cost of replacing it.